1. Field of the Invention
This invention relates to a method of forming a micro-aperture. It also relates to a projection having such a micro-aperture, to a probe or multi-probe having such a projection or projections and also to a surface scanner (surface-observing system), an aligner (exposure system) or an information processor comprising such a probe. More particularly, the present invention relates to a method of manufacturing a micro-tip for detecting or irradiating evanescent light to be used for a near-field optical microscope and to a probe having such a micro-tip.
2. Related Background Art
The invention of the scanning tunneling microscope (hereinafter referred to as STM) made it possible to visually observe the electron structure of surface atoms of an electric conductor [G. Binnig et al., Phys. Rev. Lett. 49, 57 (1982)] and hence a real space image of a specimen to be dimensionally measured with an enhanced degree of resolution regardless if the specimen is monocrystalline or noncrystalline. Since then, research efforts have been paid on the scanning probe microscope (hereinafter referred to as SPM) particularly in an attempt to look into the micro-structures of various materials.
SPMs include scanning tunneling microscopes (STMs), atomic force microscopes (AFMs) and magnetic force microscope (MFMs) that are adapted to detect the surface structure of a specimen by means of a tunneling current, an atomic force, a magnetic force or a beam of light produced when a probe having a micro-tip is brought very close to the specimen.
The scanning near-field optical microscope (hereinafter referred to as SNOM) has been developed from the STM. It can be used to examine the surface of a specimen by detecting evanescent light seeping out from the micro-aperture arranged at the sharp tip of the probe of the microscope by means of an optical probe from the surface of the specimen [Durig et al., J. Appl. Phys. 59, 3318 (1986)].
The photon STM (hereinafter referred to as PSTM) is a type of SNOM and adapted to examine the surface of a specimen by introducing a beam of light into the specimen from the backside through a prism, making the beam totally reflected by the surface of the specimen, and then detecting evanescent light seeping out from the surface of the specimen by means of an optical probe [Reddick et al., Phys. Rev. B39, 767 (1989)].
Since the resolution of an SNOM is determined as a function of the tip diameter of the optical probe, the surface of the probe is shielded against light and is typically provided with a micro-aperture at the tip thereof in an SMOM so that light may come out only through the small exit.
A number of techniques have been proposed to produce a micro-aperture. According to a proposed technique, a micro-aperture is formed by coating the intersection of cleaved planes of a transparent crystal with metal and then removing the metal from the intersection by pressing the metal-coated crossing against a very hard surface (see FIG. 1A) (European Patent EP0112402).
According to another proposed technique, a micro-aperture is formed by depositing metal on the micro-tip by evaporation only from a given direction, while rotating the optical fiber probe, to produce an area carrying no metal deposit on it (see FIG. 1B).
However, in the latter case, a micro-aperture is formed on an optical fiber probe on a one by one basis. Also, the process of forming a micro-aperture in any of the known techniques will inevitably show a poor productivity and it is difficult to realize a process that can produce a number of micro-apertures in an integrated manner.
Additionally, the known techniques are accompanied by the difficulty of precisely controlling the diameter of the micro-aperture to ensure a reliable degree of reproducibility.
In view of the above identified technological problems, it is therefore an object of the present invention to provide a method of forming a micro-aperture or micro-apertures, easily integrated on a substrate, with an enhanced degree of reproducibility, the method minimizing the variances in the diameter of the micro-apertures and achieving a high productivity in batch processes. Another object of the present invention is to provide a projection having such a micro-aperture. Still another object of the present invention is to provide a probe or a multi-probe having such a projection or projections. Still another object of the invention is to provide a surface scanner, an aligner or an information processor using such a probe.
According to a first aspect of the invention, the above first object is achieved by providing a method of forming a micro-aperture comprising steps of:
forming a projection or a dent on a substrate;
forming a film on the surface of said projection or of the opposite side of said dent so as to make the film thin at and near the tip of said projection or said dent;
etching said film to expose said tip; and
producing a micro-aperture by etching the exposed tip.
The remaining objects of the invention are achieved by providing a projection having a micro-aperture formed by the above described method, a probe having such a projection, a multi-probe having such projections formed on a substrate and a surface scanner, an aligner or an information processor comprising such a probe or a multi-probe.